The present invention generally relates to a document reading apparatus, and more particularly to a document reading apparatus which can reliably detect a data sheet and a data sheet edge in a sheet transport path of the document reading apparatus.
Conventionally, a document reading apparatus may be used as a single data reading unit, or may be used within a scanning part of a facsimile or within a copying machine. In a case of such document reading apparatus, an original document is transported one by one along a transport path to a data reading part, and an image data reading from the original document is carried out by the data reading part. For this reason, the document reading apparatus must have a data sheet detecting part for detecting a data sheet on a data sheet plate, and a sheet edge detecting part for detecting a front edge or rear edge of the data sheet being transported.
FIG. 1 shows a construction of a facsimile 1 to which a conventional document reading apparatus 2 is applied. In this document reading apparatus 2 within the facsimile 1, a data sheet sensor 3 and a data sheet edge sensor 4 are provided. A data sheet or original document on a document board is transported one by one by means of an automatic feeding unit 5 to a data reading part 6. This data reading part 6 comprises a light source 7, a pair of ejection rollers 8, a plurality of mirrors 9, 10, 11, a lens 12 and a photoconductive element 13. The data reading part 6 in the document reading apparatus 2, a data sheet on the document board is detected by the data sheet sensor 3, and then the data sheet is transported one by one by the automatic feeding unit 5 to the data reading part 6. A front edge of the data sheet and a rear edge thereof are detected by the data sheet edge sensor 4. When the front edge of the data sheet is detected, the data reading part 6 starts a data reading of the data sheet. After the rear edge of the data sheet is detected, the data reading part 6 carries out the data reading until the rear edge thereof is detected, and the data reading is ended. In FIG. 1, the facsimile 1 has a facsimile control unit 14, a roll of recording paper 15, a thermal head 16 and a platen roller 17. The direction in which a data sheet is transported by the automatic feeding unit 5 is indicated by an arrow A, and the direction in which the recording paper is transported is indicated by an arrow B.
Conventionally, a photocoupler is used for the data sheet sensor 3 and the data sheet edge sensor 4. A light beam emitted from the photocoupler is irradiated to the data sheet and a reflected light beam reflected on the data sheet is received by the photocoupler to detect the data sheet or the front edge or rear edge of the data sheet. There are another sensing units which are disclosed, for example, in Japanese Laid-Open Utility Model Application No. 54-47314 and Japanese Utility Model Publication No. 63-29332. In the case of these sensing units, a detection lever or actuator is moved by an original document when it is transported, and a movement of the detection lever or actuator is sensed by a reflection type photocoupler for detecting the original document or a front edge or rear edge of the original document.
However, there is a problem in that the photocoupler used in such a conventional document reading apparatus is expensive, and especially a harness attached to the photocoupler and a printed circuit board prepared for the photocoupler are required to make use of the photocoupler. Therefore, the product cost required for a data sheet detection and a data sheet edge detection becomes high, thereby making the cost for the document reading apparatus apparatus higher.
An improved data sheet detection method has been proposed by the same applicant, in which a solid-type image pickup element is used for data sheet detection instead of the photocoupler, this solid-type image pickup element is similar to a solid-type image pickup element used for reading image data from a data sheet. This data sheet detection method is disclosed, for example, in Japanese Laid-Open Patent Application No. 59-37763. A document reading apparatus according to the data sheet detection method as disclosed, comprises a first photoconductive element for reading image data from a data sheet and a second photoconductive element for detecting a data sheet, the second photoconductive element provided at a position apart from the first photoconductive element in a sub scan direction. An image reading and a data sheet detection are carried out in this document reading apparatus by detecting serially a signal outputted from the first photoconductive element and a signal outputted from the second photoconductive element. However, in this data sheet detection method, the first photoconductive element for reading image data and the second photoconductive element for detecting a data sheet must be placed apart form each other. Therefore, two solid-type image pickup elements which are provided on different integrated circuit chips are necessary for manufacturing such a document reading apparatus, and there is a margin of improvement of the document reading apparatus for the cost reduction. And, in the case of the above data sheet detection method, the degree of freedom to design the document reading apparatus is limited.